( 658 ) 
Chemistry. — “On miscibility in the solid aggregate condition and 
isomorphy with carbon compounds” [First communication]. 
By Dr. F. M. Janenr. (Communicated by Prof. H. W. Baknurs 
RoozrBoou). 
(Communicated in the meeting of March 25, 1905). 
Since the discovery of isomorphy by MrrsenerrieH the power of 
isomorphous compounds to form, on being mixed, a homogeneous 
solid phase of gradually-varying composition has been experimentally 
demonstrated in numerous cases. 
In recent years several investigators have started theories as to the 
course of the melting curves likely to be exhibited by such mixing- 
series, and in conjunction with the theory of the equilibrium of 
phases and with the aid of thermodynamical developments, a fairly 
clear idea has been formed of the special cases which may be 
expected to occur with substances of the said kind. 
On the other hand, it is not permissible to draw conclusions as 
to existing isomorphy, solely on account of the course of the melting 
curve or the solubility lines. Since the introduction in chemistry 
of the idea of “solid solutions”, many cases have already been 
pointed out where amorphous or even crystallised solid solutions 
exist of substances which bear either no or an unknown erystallo- 
nomic relation to each other. We have only to think for instance 
of amorphous glasses and on the other hand of the cristalline mix- 
tures of ferric-chloride and sal-ammoniac. The difficulty is felt in a 
particularly striking manner in the chemistry of the carbon compounds ; 
not only do we know continuous series of crystalline mixtures 
between morphotropously allied carbon-containing derivatives, as in 
Murumann’s terephthalic-acid derivatives, but such mixing even in 
the erystalline condition, has also been observed in the case of 
organie molecules which have little or nothing in common. 
Brunt and his collaborators, who have made a long series of eryos- 
copic determinations conclude that the most dissimilar organic sub- 
stances may yield “mixed crystals” and “solid solutions” of whose 
erystallonomie relation not only nothing as a rule is known, but of 
which the erystallographer will think the chances of isomorphy but 
very small. 
In any ease the relation existing between ““erystallonomie form- 
relation’ and “miscibility: is as yet quite unknown. If substances 
are isomorphous, that is if crystalline phases possess regulated mole- 
cular structures, which may be assumed to be formed from each 
other by a slight deformation, such phases may jointly yield a homo- 
geneous mixing-phase of variable composition and their relations 
